This proposal requests funding for a complete state of the art cryo-electron microscopy facility. The facility, including a Philips CM-12 electron microscope, a Gatan cryo-specimen stage and a tilt anti-contaminator, will be used in studies of the structure and function of a number of proteins, lipoproteins and assemblies present at membrane interfaces and in cells. Specifically, the proposed research will focus on determining the 3-dimensional structures of a) Nuclear Pore Complexes in various transport related configurations, b) the A-subunit within the cholera toxin B-pentamer associated with membranes, c) LDL and LDL-LDL receptor complexes d) assembly "mutants" of phage, M13, e) bacterial adhesion pili and f) various lectin-carbohydrate complexes. In addition the facility will support several routine electron microscopy studies, for example the morphological and size characterization of lipid emulsion systems as models for, plasma lipoproteins, lipid vesicles and cell membrane preparations. Proposed studies of the NPC will contribute to our understanding of the nuclear transport pathway and the role of the NPC in maintaining normal interphase compartmental distributions of proteins and RNPs. Three-dimensional studies of various transport-related configurations of the central transporter assembly within the NPC should allow a determination of the molecular mechanism responsible for nucleocytoplasmic transport. Three-dimensional studies of the membrane-associated form of the intact cholera toxin (A + B subunits) in ice will complement ongoing high resolution single crystal studies on" the B subunit pentamer by X-ray crystallographic methods and should yield insights into; the mechanism and chemical basis of membrane penetration by the toxin. Studies on the 3D structural organization of LDL and in particular the arrangement of the protein apoprotein B on the surface of the lipoprotein and complexes with its receptor will provide fundamental structural information essential to an understanding of the physiological and cellular processes of lipid metabolism at the molecular level. Combined structural analysis of M13 phage and bacterial pili by x-ray and neutron diffraction coupled with cryo-electron microscopy will allow a greater insight into the fundamental principles involved in the regulated assembly of helical viruses and other large structures in cells.